1. Field of the Invention
This invention is directed to improvements in filter elements for smoking articles. While the invention will be described with reference to a preferred embodiment as a cigarette filter, it will be recognized by those skilled in the art that the field is broader and includes other applications such as filters for small cigars. Moreover, recent innovations have expanded the use of smoking devices into areas such as delivery of medicaments. Examples of these applications include Gabriel U.S. Pat. No. 4,598,720 dated 8 July 1986 and European Published Application No. 0174645 to R. J. Reynolds Tobacco Company published 19 March 1986. The filter element of the invention, thus, is broadly useful for smoking articles of widely varying types and constructions which will be more apparent in light of the description which follows.
2. Description of the Prior Art
Filtered cigarettes are well known and the most common form of smoking articles. They comprise a column of tobacco and, at one end, a filter plug with the combination wrapped in a thin paper. Conventional filter plugs are formed either from compressed strips of paper or cellulose acetate. It has long been recognized that certain thermoplastic polymers possess attributes that would suggest their use as cigarette filter plug materials. For example, Buntin et al. U.S. Pat. No. 3,595,245 dated 26 July 1971 is directed to a meltblown roving of polypropylene fibers formed as a tow and processed into cigarette filter plugs. Further discussion of such polypropylene fiber cigarette filters may be found in U.S. Pat. No. 4,546,040 dated 8 Oct. 1985 to Knotek et al. and in the references cited therein at column 1, lines 44-57. In spite of such teachings, thermoplastic polymer fiber filter plugs, notably those made of polypropylene fibers, have achieved little, if any, commercial success. Common deficiencies of prior attempts to form thermoplastic fiber filter plugs have included inadequate firmness so that the filter end of the cigarette has an uncharacteristic and undesirable softness and a greater than desired pressure drop so that the smoker experiences a perceivable increase in draw resistance. It is desired, therefore, to provide filter plugs for smoking articles that take advantage of the economies of thermoplastic fiber formation and yet have improved properties overcoming these deficiencies as well as possessing other advantages.